Solving Long-Standing Meteor Mysteries

Open Access
Author:
Malhotra, Akshay
Graduate Program:
Electrical Engineering
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
June 25, 2009
Committee Members:
  • John David Mathews, Dissertation Advisor
  • John David Mathews, Committee Chair
  • James Kenneth Breakall, Committee Member
  • Julio Urbina, Committee Member
  • Hampton Nelson Shirer, Committee Member
Keywords:
  • Radio Science
  • Meteors
  • Radar
  • Aspect Sensitivity
Abstract:
Millions of meteoroids strike and disintegrate in the Earth’s upper atmosphere every day and may be seen as visible or radar meteors. Although very few of the these foreign bodies actually make it to the surface of the Earth, they have been known to cause damage to satellites and are also the only known source (except for spacecraft debris) of metallic ions in the upper atmosphere, thus being responsible for various atmospheric phenomena. Despite these meteor echoes being studied using radars for close to a century now, some long–standing unsolved mysteries still remain in the field—what causes some of the meteor trails to last for so much longer compared with the other trails? Are meteors really responsible for the formation of Sporadic-E, an altitude–thin ionospheric layer? If yes, then why has there been no evidence of a direct relationship between the two despite numerous attempts since the 1930s? Using data collected from the Jicamarca Radar Observatory in Peru, we answer all of the above questions and solve these long–standing mysteries. Our results emphasize the importance of paying careful attention and due consideration to radio science issues while analyzing radar meteor echoes. It is found that the viewing geometry, i.e. the aspect sensitivity of meteor echoes, is also the primary constraint in observing long–duration meteor trails and almost all of the long duration echoes seem to originate from the k⊥B region (k = wave vector, B = geomagnetic field) of the radar. This result is extremely significant because it raises questions about the observed durations of all Range Spread Trail Echoes (RSTE): the same meteor event could be simultaneously observed as a long duration trail (greater than 15 seconds) from one radar and a short duration trail from another radar. These claims are supported by observations from the first-ever multi-static common volume radar observations of RSTEs. These results also provide new insights into the physical structure of the plasma giving rise to these echoes and also establish a firmer basis for the modeling of the plasma processes that cause meteor trails to become field-aligned while underlining the importance of carefully distinguishing event radio science as a prelude to specifying the role of these plasma processes.